Through the Looking Glass: Chirocaine vs Bupivicaine. St.Emlyn’s

I’ve seen a few paediatric femoral shaft fractures in the last couple of years, and while they always make my spidey-sense tingle for non-accidental injury, most (even the spiral fractures) have been explained away by plausible mechanisms of injury; they are usually late toddling age, have got their feet stuck, twisted and fallen over.

The way I’ve managed these patients has changed with my experience and skill level; as an SHO I looked at them with sympathy while the oramorph, ibuprofen and paracetamol were absorbed slowly from their (no doubt static) GI tracts. As a registrar, they now get a squirt of intranasal diamorphine and an application of ametop over the ipsilateral groin, in anticipation of an ultrasound-guided femoral nerve block when they return from x-ray. I mix up a 50:50 solution of 1% lidocaine with 0.5% bupivacaine and, before ultrasound guidance, used 1mL per year of age. It works out as less than 2mg/kg of lidocaine (usually) and less than 1mg/kg bupivacaine – so relatively small doses. I’ve done it a few times, and it works pretty well, especially in combination with a Thomas splint. The great thing about ultrasound-guidance besides lower failure rates is that you can use even smaller drug volumes – it ends up more like 0.5mL per year of age.

So as I examined the two year old, who was refusing to weight bear, with little deformity to his leg but clear femoral tenderness, I reached for the trusty bupivacaine/lidocaine combination to make splint application less of an auditory assault. But shock! Horror! No bupivacaine!

Instead, there was chirocaine – which completely confused me, as I had no idea what it was (and there was apparently no bupivacaine to be had anywhere). I asked around – and no-one seemed to be entirely sure how the two drugs related to one another. So, after some research, I thought I’d share.

Chirocaine (levobupivacaine), as you may know (I didn’t), is “the pure S-enantiomer” of bupivacaine. The story is that some drugs exist in a 50:50 (racaemic) mixture of two stereo-isomers; molecules which are mirror images of one another. Where the mirror images cannot be superimposed, the molecules are said to be chiral, and the most common cause for this is an asymmetrical carbon atom. There is a right (dex-, or d-) and left (levo-, or l-) version of the molecules which cannot be made symmetrical no matter the orientation in the same way as your left foot just doesn’t fit in your right shoe [NB: an important differential in the non-weight bearing child]. Where drugs bind to receptors, one isomer may be able to bind, while the other cannot – or may generate alternative effects.

You probably knew this already, right? Every time you prescribe levothyroxine, esomeprazole, escitalopram or levofloxacin, you think proudly about how you are selecting out the correct isomer for your patient, yes? And how you are therefore giving half the dose, as they aren’t getting the 50% of isomers which don’t give a clinical effect? Well, it doesn’t quite work as predictably as that. In fact, in some cases the dose is significantly lower for the same clinical effect (notably escitalopram, 30 times more potent than citalopram) and in others confers no therapeutic advantage at equivalent doses (see esomeprazole) or may even be harmful (see thalidomide).

So what’s so special about chirocaine? It’s twice the price of standard bupivacaine per 10mL ampule, so it’s twice as good, isn’t it?

Well, no – it seems to be equivalent at providing analgesia in a variety of blocks (caudal, ilioinguinial, rectus sheath… The list goes on…), but every study is focussed on the reduction in adverse (cardiac) effects with levobupivacaine. It seems the rationale for selecting out this isomer is reducing cardiac toxicity. Where does this come from?

Most data comes from animal studies (in case you didn’t know, children are no more little adults than they are little rats, pigs, rabbits…).

You have to dig quite deep for original studies. All roads seem to lead back to this one paper. 14 healthy, adult, male subjects were injected with bupivacaine or levobupivacaine infusion and asked “do you have any symptoms?”. OK, let’s be fair, they’ve powered the study to detect a 10% difference in their primary outcome (stroke volume), but their bottom line conclusion is “that levobupivacaine may be a safer drug than rac-bupivacaine for procedures requiring high doses of local anaesthetic.” So not really our fractured femur toddlers, then.

Which brings us back to the beginning. Studies in children have suggested that levobupivacaine produces equivalent anaesthetic efficacy, but what they haven’t done is convince me that we should ditch bupivacaine when we are using such tiny doses. It’s cheaper, and with ultrasound guidance we can use a miniscule amount to achieve local anaesthesia long enough to reduce the fracture in a Thomas splint.

So the bottom line is this; use what you’ve got unless there’s specific cardiac risk for your paed patient, and using 50:50 with 0.5% chirocaine provides the same analgesia as bupivacaine (in our hospital the maximum dosing for ilioinguinal block is apparently 1.25mg/kg/side). Whatever you use, do the block; your patients will probably thank you (but we might have to wait to find out).

Natalie May

Ref

A comparison of the cardiovascular effects of levobupivicane and rac-bupivicane following intravenous administration to healthy volunteers. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1873676/pdf/bcp0046-0245.pdf

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Posted by Natalie May

Dr. Natalie May, MBChB, MPHe, MSc, PGCert Medical Education, FRCEM, FACEM is section lead for paediatrics and medical education. She is an Editorial Board Member of the St Emlyn’s blog and podcast. She is a specialist in Emergency Medicine (Australia) and a Specialist in Emergency Medicine with Paediatric Emergency Medicine (UK). She works as Staff Specialist in Prehospital and Retrieval Medicine with the Ambulance Service of New South Wales (aka Sydney HEMS). She also works as aStaff Specialist, Emergency Medicine, St George Hospital (South Eastern Sydney Local Health District). Her research interests include medical education, particularly feedback; gender inequity in healthcare; paediatric emergency medicine. You can find her on twitter as @_NMay

Question – do you think mixing with liGNocaine (that’s lidocaine to some) is really necessary. The difference in onset times for ring blocks of the finger is minimal and I wonder if there is a clinically significant difference for the Femoral blocks by mixing the two agents. If we had to go for longevity of block vs a couple of minutes in difference of onset I might opt for the former.

Great article natalie – thank you….. interestingly science boffins are using levo vs dextro molecule orientation to investigate the origins of life…earthly vs extra-terrestrial being possibly different – may help you in paediatrics??!

On a, meh, perhaps more relevant note – I ask the same question as simon…..Do you find a cocktail of lignocaine + bupivo/chiro-caine, gives a more positive analgesic experience? Just interested.

Thanks for the interest and the comments, guys. Glad you appreciate my love of Lewis Carroll and on the lido/ligno issue – what does it say on the ampoule?!

Serious questions now; interesting thoughts. I could certainly argue the case for longer vs shorter acting local anaesthesia; in my experience the block provides good pain relief for getting the Thomas splint on but finding the appropriately sized splint and related paraphernalia can take a while!

Kids seem to tolerate the block but probably only for a single attempt approach; so you have to be sure that what you give is going to work the first time. Local anaesthetic agents are pretty reliable so it’s not as though one is likely to “not work”, but kids are also less likely to stay still while you perform the block, so the smaller the actual LA dose you can give, the better. Lidocaine is generally accepted as presenting a lower risk of cardiovascular side effects in kids, which makes me feel better, but then as we have already established, the doses we are giving are pretty small.

I don’t have explicit experiences sufficient to answer the question as to the block effectiveness, but the assumption I am making is that toxic effects are not cumulative when you mix two agents. I have had a look and I really can’t find a definitive answer. A rat study (how I love those! http://www.biomed.cas.cz/physiolres/pdf/59%20Suppl%201/59_S65.pdf ) seems to suggest toxicity is lessened in a lido/bupivacaine mix.

My thinking is that the best block approach would be:
– suspicion of femoral shaft fracture: intranasal diamorphine/equivalent non-IV analgesia
– identify the femoral fracture on ultrasound (http://www.bjj.boneandjoint.org.uk/content/82-B/8/1170.full.pdf and http://www.ncbi.nlm.nih.gov/pubmed/18516770 )
– ametop to ipsilateral groin site with explanation to parents
– formal radiography (maybe one day this step will disappear?)
– femoral nerve block
– splint application
– happy child, playing with toys around the splint (as happened in the case in question)

However, as to whether you use a pure chiro/bupivacaine block or mix it up, the need for a good quality RCT has emerged!

Agreed, and worth working through those articles to build the bigger picture. I must admit to preferring to use just Bupivicaine for most blocks where long term analgesia is needed these days. As you say though, the evidence is somewhat scanty and here and it’s just a personal opinion.
S

Been using a lidocaine/bupivicaine mix for haematoma blocks in wrist fractures for as long as I can remember. Not in any way evidence based and is probably based on me being pretty rubbish reducing Colles fractures in the distant past and I wanted enough long acting block to have another go if required. As one would expect, I got better at doing the reductions but kept the same technique because it worked pretty well.

I still recall as a young registrar listening to the squeals of patients behind a curtain having had a poor block and a brutal reduction and it scarred me – so it was 1% lido to skin and soft tissue, find haematoma (and I mean REALLY find it), more lido, detach syringe, replace with bupivicaine, more to haematoma. Don’t use bupivicane only because, well, I’ve “always done it that way and it seems to work very well” – ahem. Not met anyone else who does this… I’m sure others recommend Bier’s blocks, procedural sedation etc and I might be old fashioned… comments welcome.

Always had mixed results with femoral n. blocks, all in adults it must be said. Haven’t done enough to be comfortable / proficient (not that many femoral fractures floating around here) – must go on that regional anaesthesia course I’ve been meaning to go on for oooh, 5 years?

[…] (particularly with local anaesthetics) you can do these things in combination – for example, for the child with a femoral shaft fracture: intranasal diamorphine, oral paracetamol or ibuprofen, topical local anaesthetic followed by an […]